2.11.2 Downgrading MySQL

This section describes what to do to downgrade to an older MySQL
version, in the unlikely case that the previous version worked
better than the new one.

It is always a good idea to make a backup beforehand, in case a
downgrade fails and leaves the instance in an unusable state.

To downgrade between General Availability (GA) status versions
within the same release series, typically you just install the new
binaries on top of the old ones and do not make any changes to the
databases.

Downgrades between milestone releases (or from a GA release to a
milestone release) within the same release series are not
supported and you may encounter issues.

The following items form a checklist of things to do whenever you
perform a downgrade:

Read the upgrading section for the release series from which
you are downgrading to be sure that it does not have any
features you really need. See Section 2.11.1, “Upgrading MySQL”.

If there is a downgrading section for that version, read that
as well.

To see which new features were added between the version to
which you are downgrading and your current version, see the
Release
Notes.

A typical symptom of a downward-incompatible table format change
when you downgrade is that you cannot open tables. In that case,
use the following procedure:

Stop the older MySQL server that you are downgrading to.

Restart the newer MySQL server you are downgrading from.

Dump any tables that were inaccessible to the older server by
using mysqldump to create a dump file.

Stop the newer MySQL server and restart the older one.

Reload the dump file into the older server. Your tables should
be accessible.

If system tables in the mysql database changed,
downgrading might introduce some loss of functionality or require
some adjustments. Here are some examples:

Trigger creation requires the TRIGGER
privilege as of MySQL 5.1. In MySQL 5.0, there is no
TRIGGER privilege and
SUPER is required instead. If you downgrade
from MySQL 5.1 to 5.0, you will need to give the
SUPER privilege to those accounts that had
the TRIGGER privilege in 5.1.

Triggers were added in MySQL 5.0, so if you downgrade from 5.0
to 4.1, you cannot use triggers at all.

The mysql.proc.comment column definition
changed between MySQL 5.1 and 5.5. After a downgrade from 5.5
to 5.1, this table is seen as corrupt and in need of repair.
To workaround this problem, execute
mysql_upgrade from the version of MySQL to
which you downgraded.